In general, various kinds of stents have been used to expand the stenosed part of the bile duct, the esophagus, the respiratory tract, the ureter or other bodily organs. The stenosed part is generated by a cancer or other diseases or by an inflammation attributable to the use of an endoscope in medical treatment.
Along with the development of medical science, the stents are used in many different fields such as endoscopic retrograde biliary drainage (ERBD), endoscopic retrograde pancreatic drainage (ERPD) and so forth.
One typical example of the conventional stents is illustrated in FIGS. 1 and 2. The stent 7 is produced by interlacing super-elastic shape-memory alloy wires 1 into a hollow cylindrical net body 3 with a multiplicity of rhombic meshes 2.
The stent 7 shown in FIGS. 1 and 2 is inserted into the bile duct 6 extending between the liver and the duodenum 5 through the use of a catheter (not shown). The stent 7 thus inserted serves to expand the stenosed part 60 of the bile duct 6, thereby assuring smooth flow of bile juice into the duodenum 5.
The stent 7 is situated in place so that a portion thereof can protrude into the duodenum 5 through the Oddi's sphincter 6a of the bile duct 6. If the stent 7 protrudes a short distance into the duodenum 5 as illustrated in FIG. 1, the food passing through the duodenum 5 may flow backwards into the bile duct 6. In contrast, if the stent 7 protrudes a long distance into the duodenum 5 as illustrated in FIG. 2, the particles 70 of food may be caught in the meshes 2 of the protruding portion of the stent 7. This may sometimes leads to a problem in that the outlet of the bile duct 6 clogs with the particles 70 of food, consequently hindering smooth discharge of bile juice.